The invention relates to a resistance seam welding machine, particularly for the longitudinal seam welding of can bodies, having two electrode rollers arranged one above the other, with a pivotally mounted arm which carries the upper electrode roller and guides it vertically and in the welding direction, and a lower arm which carries the lower electrode roller, and having flexible current leads in the current supply to the upper electrode roller.
In a known resistance seam welding machine of this kind (DE-PS 37 10 875), the pivotally mounted arm which carries and guides the upper electrode roller is constructed in the form of a wishbone from a stirrup and a pendulum arm, each of which is pivotally mounted at one end on the machine frame and which are articulated on one another at the other end, near the upper electrode roller. The pendulum arm has a mounting flange for the upper electrode roller at the other end and is rotatably mounted at the one end in a pendulum roller head by means of rolling bearings. Also secured to this end of the pendulum arm is a toothed rim through which a chain can set the pendulum arm and hence the upper electrode roller in rotation. The pendulum roller head is built on the principle of a counterpoised balance so that its pendulum bearing arrangement carries the whole weight and the upper electrode roller rests on the lower electrode roller practically without any weight. In order to adjust a certain pressure, a spring presses from above on the shaft of the upper electrode roller. The supply line leading from the welding transformer to the upper electrode roller comprises a busbar and the pendulum roller head, which are connected to one another for electrical conduction by flexible current leads. An annular chamber filled with liquid metal is disposed between the pendulum roller head and the pendulum arm for the current transmission. The current leads consist of woven flex, that is to say of limp material which is flexible in any direction because the current leads should hinder as little as possible the free mobility of the pendulum roller head in relation to the busbar.
Although the construction of the arm with the pendulum roller head, as provided in this known resistance seam welding machine, is complicated and expensive, nevertheless in heavy-duty machines it guarantees a satisfactory weld quality, particularly a uniformly satisfactory weld quality over the whole length of the longitudinal seams of can bodies. In simpler resistance seam welding machines which work at lower welding speeds than such heavy-duty machines, it would be an advantage from the point of view of cost if a more simple bearing arrangement could be provided for the upper electrode roller without the quality of the weld being impaired as a result. If the pendulum roller head were simply omitted, the said stirrup would have to be constructed in the manner of the said busbar as a result of which the advantage of the small moving mass in the region of the upper electrode roller and its great vertical mobility would be lost. In addition, resilient current leads would have to be provided which would likewise have to restrict the vertical mobility of the upper electrode roller as little as possible. Avoiding all these problems would require an expensive construction which would cancel out the savings aimed at by omitting the pendulum roller head. Finally, as a result of the absence of the pendulum roller head, the simple possibility for the rotary drive of the upper electrode roller would also cease to exist.